Fluid heating apparatus

ABSTRACT

A fluid tank, with an inlet and an outlet, is provided with first heating means for heating the fluid in the tank to a first temperature and a second heating means for heating the fluid to a second temperature which is lower than the first temperature. A thermostatic switch is disposed to be responsive to the temperature of the fluid in the tank outlet to enable the first heating means only when the temperature in the outlet is above a predetermined level. The fluid in the tank is maintained at a low temperature during periods of non-use, and at an increased temperature only during periods of use, thus economizing on heating energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is in the field of fluid heating apparatus such as awater heater for household and other uses.

2. Description of the Prior Art

Prior art systems for heating fluid have various combinations ofthermostatic switches and heating elements to provide adequate supply ondemand together with a minimum of energy consumption. In hot waterheaters, for example, multiple heating elements and thermostatic switchdevices have been used. However, due to the condtradictory objectives ofproviding hot water on demand and economizing on heating energy duringperiods of non-use, or low-use, such efforts have been compromises whichhave not been entirely satisfactory.

SUMMARY OF THE INVENTION

A water tank has a cold water inelt pipe and a hot water outlet pipe andis provided with a first heating element for heating the water in thetank. The first element has, in the energizing circuit thereof, abimetallic thermostatic switch responsive to the temperature of thewater in the tank. The switch closes when the water temperature is belowa given temperature, such as 145° F., and opens when the watertemperature is above such given temperature. A second heating elementfor heating the water in the tank is provided and is responsive to theoperation of a second bimetallic switch which closes when the watertemperature is below a given temperature, such as 115° F. and opens whenthe water temperature is above such given temperature. A thirdbimetallic thermostatic switch senses the temperature in the outletpipe, opening when the water is below a given temperature, such as 90°F., and closing when the water temperature is above such giventemperature. A solenoid switch in the circuit of the first heatingelement is responsive to the third bimetallic switch, closing when thethird switch is closed and opening when the third switch is opened. Thesolenoid switch when closed enables the first heating element forenergization when the first thermostatic switch closes.

During periods of non-use of heated water from the tank, the temperatureof the water in the outlet pipe will drop since the water in that pipewill lose its heat to the ambient air. This opens the third bimetallicswitch and the solenoid switch thus preventing energization of the firstheating element even though the first bimetallic switch is closed.Therefore, the only energy for heating the water in the tank is thesecond heating element which heats the water to a lower temperatureduring such periods of non-use. Thus a substantial savings of heatingenergy is realized since in the normal household, hot water demands aremade on a cyclical basis, periods of non-use or low-use predominating.However, during periods of hot water usage, the temperature in the hotwater outlet will increase to a level above 90° F. due to the heatedwater from the tank passing therethrough. At this point, the thirdbimetallic switch will close energizing and closing the solenoid switch,enabling the first heating element which is a relatively high energy,fast heating element to quickly raise the water temperature in the tankduring such periods of use. Thus, during periods of hot water use thetank temerature is high and during periods of non-use, the tank watertemperature is low, resulting in substantial heating energy savings.

If desired, and where required by local utility regulations, the secondthermostatic switch may be an interlock switch so that both the firstheating element and the second heating element cannot be energized atthe same time. This may be accomplished by making the secondthermostatic element a single pole, double throw switch which closesonly one of the heating element energizing circuits at a time. Also, athermostatic safety switch responsive to tank water temperature willopen the power circuit for energizing both heating elements when thetank water temperature exceeds a given level. The safety switch must bemanually reset, which can be done when the water temperature falls belowa maximum level. This invention may also be utilized in low volume,quick heating hot water systems which are known to the art.

It is therefore an object of this invention to provide an energy savingfluid heating apparatus.

It is a further object of this invention to provide an apparatus of theforegoing object for sensing the fluid temperature in the fluid outletto enable a fluid heating element for heating tank fluids.

It is a further object to provide in the apparatus of the foregoingobject multiple heating elements for heating the fluid to first andsecond temperatures, the higher temperature element being enabled onlyduring periods of fluid use and the lower temperature element beingenabled during periods of fluid non-use.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic circuit diagram showing a first preferredembodiment with the water tank shown in phantom;

FIG. 1a is a schematic diagram of the safety switch in an opencondition;

FIG. 2 is a schematic circuit diagram showing a second embodiment withthe water tank shown in phantom; and

FIG. 3 is a partially schematic sectioned view of a thermostatic switchused in the embodiments of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, a first preferred embodiment is shownschematically in FIG. 1, FIG. 1a and FIG. 3. A hot water tank 20 is shonin phantom in FIG. 1 and has water inlet pipe 22 and water outlet pipe24. The water within tank 20 in the embodiments in this invention isheated by electrical heating elements 26 and 28, but it is to beunderstood that this invention applies as well to other ways and meansof water heating, such as by gas. Electrical power for providing heatingenergy to elements 26 and 28 is connected to terminals 30 and 32 and maybe conventionally available household power such as 220 volts, 60 Hz.Terminal 32 is connected by way of line 34 to relay switch terminal 36.Switch terminal 38 is connected by line 40 to a first bimetallic switch41 having terminals 42 and 44 and bimetallic element 46 which connectselectrically terminals 42 and 44 when the water temperature in tank 20is below a given temperature, such as 145° F. Bimetallic switch 41 maybe any suitable commercially available bimetallic switch. Terminal 44 isconnected through heating element 26 to a second conventional bimetallicthermostatic switch 47 and has terminals 48 and 50. A bimetallic switchelement 52 is mounted at one end to terminal 54 which is connectedthrough safety switch assembly 56 to terminal 30. Bimetallic element 52will switch from terminal 50 to terminal 48 whenever the tank watertemperature exceeds a given level, such as 115° F, which is lower thanthat level at which switch 41 opens. Thus element 52 and terminals 48and 50 form a single pole, double-throw bimetallic thermostatic switch.When element 52 is contacting terminal 50, a circuit is establishedbetween terminals 30 and 32 through heating element 28 and switch 56.When element 52 is in its alternate position, in contact with terminal48, a circuit is established between terminals 30 and 32 through heatingelement 26, switch 56, element 46, and relay terminals 36 and 38, whenthey are closed by circuitry later described.

Switch 56 is a conventional safety switch. Many utility regulationsrequire such a switch to open the circuit to the heating elements whenthe tank water temperature exceeds a given temperature. The circuit willremain open until it is manually reset. The bimetallic element 58 ismechanically mounted at each of its ends to fixed mounting points 60 and62. The center of element 58 is mechanically coupled to an insulativepin 64 which is in fixed relation to electrically conductive contact 66.Contact 66 in its lower position closes terminals 68 and 70. Insulativebutton 72 is an extension of pin 64 and extends to the exterior of tank20 so that it is manually accessible for reasons later described. Plate66 is spring urged by springs 74 and 76. In normal operation of thetank, switch 56 will be in its "closed" position wherein contact 66closes terminals 68 and 70. Prior to the tank water temperature reachinga dangerous level, element 58 will change position, to that shown inFIG. 1a, forcing plate 66 upwardly against the force of springs 74 and76. This opens the circuit to both heating elements 26 and 28 whichcircuits will remain open until button 72 is manually depressed,restoring element 58 to its position, shown in FIG. 1. In other words,even if the tank water temperature should fall below a predeterminedmaximum, the switch 56 will still remain open until button 72 ismanually depressed.

A third thermostatic bimetallic switch 80 is operable by the temperatureof the water in pipe 24.

Referring to FIG. 3, a cylindrical plug 82 of a high heat conductivitymaterial, such as copper, is thermally attached to pipe 24, which ispreferably of a high heat conductivity material such as copper.Physically attached to plug 82 is bimetallic switch element 84 mountedin a housing 86. Pin 88 is attached to and between elements 84 andresilient upper switch blade 90. Blade 90 carries contact 91 at its end,is mounted at 92 and is electrically connected to line 94. Lowerresilient switch blade 96 carries contact 97 at its end, is mounted at98 and electrically connected to line 100. When the water in pipe 24 isbelow a given temperature, such as 90° F., element 84 will maintainblade 90 in its upper position, so that electrical contacts 91 and 97are open. However, when the water temperature in pipe 24 exceeds 90° F.,as it would during hot water usage due to the heated water from tank 20passing through pipe 24, element 84 will move blade 90 to a downwardposition closing contacts 91 and 97. The switch 80 is positioned on pipe24 far enough removed from tank 20 that during prolonged periods of nohot water being drawn, the pipe 24 as well as the switch 80 will cooldown to a temperature below 90° F.

Referring to FIG. 1, terminals 102 and 104 are connected to an availablehousehold voltage supply, such as 220 volts, 60 Hz, placing this voltageacross primary 106 of transformer 108. Secondary 110 reduces the voltageto approximately 24 volts which is placed across solenoid coil 112 whencontacts 91 and 97 are closed. When coil 112 is so energized, armature114 raises contact plate 116 closing contacts 36 and 28 and enablingheating element 26.

In operation of the embodiment of FIG. 1, and assuming a condition ofprolonged non-hot water usage, the temperture of the water in pipe 24will be low, below 90° F., since its heat will have dissipated to theambient air. In this condition, bimetallic thermostatic element 84 willbe in its upper position, FIG. 3, and contacts 91 and 97 will be open.This opens the circuit of secondary 110 and armature 114 is in its lowerposition, FIG. 1, and contacts 36 and 38 will be open. Therefore, eventhough element 46 has closed contacts 42 and 44, since the tank watertemperature is considerably below 145° F., heating element 26 will bedeenergized. Heating element 28, however, will be energized a sufficientportion of the time to maintain the tank water temperature atapproximately 115° F. This is because element 52 will make electricalcontact with terminal 50 whenever the water temperature drops below 115°F.

When hot water usage increases, the water temperature in pipe 24 willrise to approximately 115° F., the tank water temperature, and willclose contacts 91 and 97, energizing solenoid coil 112 from the voltagedeveloped across secondary 110, whereby conductive plate 116 will closeswitch terminals 36 and 38 enabling element 26. As mentioned, bimetallicswitch 46 already has closed terminals 42 and 44. If switch element 52is in contact with terminal 48, indicating the water temperature isabove 115° F., or when element 52 contacts terminal 48, element 26 willbe energized since a current path will be completed between terminals 30and 32. The tank water will quickly rise to 145° F. due to energizationof heating element 26 which is a heavy duty, high energy, fast actingelement. This will maintain switch element 52 in contact with terminal48 and switch element 46 will maintain contacts 42 and 44 closed untilthe tank water temperature exceeds 145° F. at which time switch element46 will open the contact between terminals 42 and 44.

If during the increased hot water usage, which would close contacts 91and 97, element 52 is on contact 50, indicating that element 28 is beingenergized, it will be necessary to wait until the tank water temperatureexceeds 115° F. and element 52 makes contact with contact 48 beforeelement 26 is energized. This generally will be on only a short while.With the circuitry of FIG. 1, element 52 provides an interlockpreventing both heating elements 26 and 28 from being energized at thesame time, thereby reducing the peak power requirements.

Referring to FIG. 2, similar elements will carry similar referencenumerals to those in FIG. 1. In the embodiment shown in FIG. 2 there isno interlock and heating elements 26 and 28 may both be energizedmomentarily during hot water usage whereas only element 28 is energizedduring non-hot water usage. Safety switch 56 operates in identically thesame manner as switch 56 in FIG. 1. Also, thermostatic bimetallic switchelement 46 operates in the manner of element 46 in FIG. 1 as doesbimetallic thermostatic assembly 80. All the remaining elements alsooperate identically with the exception that when switch element 52breaks connection with contact 50, it does not make contact with aconductor through which element 26 is energized since element 26 isconnected directly to switch 56. In operation of the embodiment of FIG.2, during prolonged periods of non-hot water usage, the temperature ofthe water in pipe 24 will be below 90° F., so that contacts 91 and 97will be open. Solenoid 112 will be inactive and plate contact 116 willbe in its lower position, so that terminals 36 and 38 will not beelectrically connected. This will disable heating element 26, whether ornot element 46 has closed contacts 42 and 44. During this period, tankwater temperature is kept approximately at 115° F., since below thattemperature element 52 will make contact between contacts 50 and 54energizing heating element 28. However, during periods of hot waterusage, the temperature of the water in pipe 24 will rise causingcontacts 91 and 97 to close, energizing solenoid coil 112 due to thevoltage developed across secondary 110 in transformer 108, raisingarmature 114 so that plate 116 makes electrical contact betweenterminals 36 and 38 thus enabling the heating circuit for element 26.Since the tank water temperature at this point is below 145° F., element46 will be in the switch position to make electrical contact betweenterminals 42 and 44 energizing element 26. Elements 26 and 28 will bothbe energized if the water temperature is below 115° F. Element 52 willopen when the water tank temperature exceeds 115° F. and only element 26will provide the heating for tank 20 after that point.

In this embodiment, as in the embodiment of FIG. 1, the tank watertemperature is maintained approximately at 115° F. during non-usage.During hot water usage, tank water temperature is increased to 145° F.Therefore, during periods of non-hot water use such as at nighttime andduring the day, the tank water temperature will be at 115° F. instead of145° F., providing a considerable saving in heating energy. Asmentioned, this invention may be used equally well as gas fired heatersand also may be used in quick heating, low capacity water tanks.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of the invention.

What is claimed is:
 1. Fluid heating apparatus comprising:a fluid tankhaving a fluid outlet through which fluid from the tank may flow, saidoutlet being in heatdissipating relation to a heat energy absorbingmedium; first heating means for heating the fluid in said tank to afirst temperature; and control means for sensing the outlet fluidtemperature and for activating said first heating means responsive tofluid temperatures above a predetermined level in said outlet and fordeactivating said heating means in response to fluid temperatures insaid outlet below said level.
 2. Fluid heating apparatus according toclaim 1 including second heating means for heating the fluid in saidtank to a second temperature lower than said first temperature and atleast as high as said predetermined level.
 3. Fluid heating apparatusaccording to claim 2 including interlock means for preventing both saidfirst and second heating means from being energized at the same time. 4.Fluid heating apparatus according to claim 2 wherein said first heatingmeans includes a first thermostatic switch means actuably responsive totemperatures above the first fluid temperature in said tank fordeactivating said first heating means;said second heating means includesa second thermostatic switch means actuably responsive to temperturesabove the second fluid temperature in said tank for deactivating thesecond heating means; and said control means includes a thirdthermostatic switch means actuably responsive to temperatures below athird temperature of the fluid in said outlet, for deactivating saidfirst heating means, said third temperature being lower than said secondtemperature.
 5. Fluid heating apparatus according to claim 4 whereinsaid first heating means includes a first heating element circuit andsaid second heating means includes a second heating element circuit;saidsecond thermostatic switch being a single pole double throw switchhaving a first switch position activating said first circuit anddeactivating said second circuit and a second switch position activatingsaid second circuit and deactivating said first circuit.
 6. Fluidheating apparatus according to claim 4 wherein said control meansfurther comprises a solenoid switch responsive to actuation of saidthird thermostatic switch for activating said first heating means whenthe temperature in said outlet is above said third temperature. 7.Apparatus for use with a fluid heating tank having fluid outlet inheat-dissipating relation to a heat absorbing medium and a heatingelement comprising;first means for thermally engaging the fluid outletand sensing the temperature of the fluid in the outlet, and forproviding a signal when said temperature is above a predetermined level;second means responsive to said first means signal for activating theheating element in the tank.
 8. Apparatus of claim 7 wherein said firstmeans comprises a thermostatic switch actuably responsive to thetemperature of the fluid in the outlet to provide said first meanssignal.
 9. Apparatus of claim 8 wherein said second means comprises asolenoid switch actuably responsive to said first means signal foractivating the heating element when the temperature in the outlet isabove a predetermined level.